It is known that one may regulate or control the combustion process of an internal combustion engine. The fuel usage of a Diesel engine, for example, may be optimized, and the noise level may be lowered by the regulation of the fuel injection. The emission of soot and NOx may also be reduced by such a regulation. The engine regulation is preferably based on the pressure conditions prevailing in the combustion chamber, which are recorded with the aid of a combustion chamber pressure sensor. Such a sensor must not have too large a dimension, and has to have good thermal stability while having sufficient sensitivity.
Combustion chamber pressure sensors are known that are equipped with a transformer element in the form of a piezoelectric monocrystal, such as quartz or langasite, or a piezoceramic, such as PZT or BIT. Monocrystals require costly mechanical processing, and, as a rule, they have a relatively low measuring sensitivity. The piezoceramics used alternatively do have a high sensitivity, but hysteresis effects and aging effects tend to occur in their case.
Besides these, piezoresistive combustion chamber pressure sensors are known, which include metal strain gauges or Si transformer elements. Metal-based strain gauges have good thermal stability, but, because of their low sensitivity and relatively large dimensions, they are not optimally suited for use in a combustion chamber pressure sensor of an internal combustion engine. Pressure sensors based on silicon have relatively great sensitivity, but are only usable up to temperatures of ca. 140° C.